Impact of Manure on Soil pH

A growing issue in the portions of our region is manure applications leading to unexpected or undesirable increases in soil pH. The secondary challenge is that once this issue is identified, and manure applications have been stopped, the soil pH will continue to increase for several more years.

This situation arises with the use of sand bedded dairy manure or layer poultry litter. Often the sand used to bed dairy cows is not actually silica sand, rather limestone (calcium/magnesium carbonate) sand. Any sand passing through separation processes functions the same as course lime.

Layer chicken flocks have calcium carbonate added to their diets to support eggshell formation and avoid calcium deficiencies in the hens. The excess calcium carbonate passes through the digestive track of the bird and feed waste is added to the layer litter. Broken eggs can also be in the litter from accidental breaks in the layer barn. If the layer operation produces liquid egg materials, the eggshells are often added back into the layer litter for land application.

The bedding sand, calcium carbonate feed additive, and eggshells are slow to dissolve and increase soil pH. It often goes un-noticed for several years of application. However once the rise in soil pH is noted, the soil pH will continue to increase for several years after application of the materials has stopped.

The pH increase of these materials is also a very useful tool when used on low pH soils. To better estimate the impact of these manures on soil pH we can test the manures for CCE (calcium carbonate equivalent) the same as a ag lime. While the interpretation of the CCE data is not defined, it does give a relative understanding how quickly and severely the soil pH might increase. For more information on testing the CCE of manures, contact your ALGL regional agronomist.

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